1) Field of the Invention
The invention relates to a biaxially oriented film based on propylene polymers containing an inorganic particulate neutralizing agent coated with a hydrophobic coating to improve slip properties.
2) Prior Art
Even ultrapure raw materials for producing films of this kind contain a remainder of catalyst residues from the polymerization. Such catalyst constituents are, in particular, compounds based on aluminum, magnesium and chlorine.
When raw material is used to produce films, the active chlorine compounds present in the raw material must be neutralized. To effect neutralization, calcium stearate, tripotassium citrate or hydrotalcite are usually added to the polypropylene based film raw materials. However, these neutralizing agents have the disadvantage that the products formed in the course of the neutralization evaporate and lead to undesirable deposits on the machinery used in film production and processing. These deposits can drip as waxy droplets onto the film and thereby distinctly impair its quality. In other cases, the color quality of the film is reduced as a consequence of yellowing.
It is therefore an object of the present invention to provide a biaxially oriented film based on polyolefins which is free of the above-mentioned disadvantages. The purpose of the invention is thus to eliminate the danger of wax spots forming on the film surface in the course of film production and film processing.
Under a non-published proposal (German Application P 38 05 165.6), 0.005-0.5 percent by weight of carbonate particles are used as neutralizing agent in a film based on propylene polymers. Since this film is intended for use as an electrical insulating film, the film raw material is free of lubricants and does not contain any ionic constituents. The resulting film has improved electrical properties, its surface offers good adhesion to metal layers, and no wax spots are formed on it.
As has now been found, the use of carbonate particles in packaging films and industrial films based on polyolefins, which unlike electrical insulating films usually incorporate antistatic and lubricant additives, results in distinctly low performance with respect to lubricating and antistatic properties.
It is therefore a further object to provide a film containing a neutralizing agent which neither leads to the formation of wax spots, nor has an adverse effect on the effectiveness of the lubricating and antistatic additives required.